Binary string to byte[] in C++?

Question

I'm using QString in Qt actually. So if there's a straightforward function please tell me:)

What I'm thinking of doing is storing a binary string into a file byte by byte:

QString code = "0110010101010100111010 /*...still lots of 0s & 1s here..*/";
ofstream out(/*...init the out file here...*/);
for(; code.length() / 8 > 0; code.remove(0, 8))    //a byte is 8 bits
{
    BYTE b = QStringToByte(/*...the first 8 bits of the code left...*/);
    out.write((char *)(&b), 1);
}
/*...deal with the rest less than 8 bits here...*/

How should I write my QStringToByte() function?

BYTE QStringToByte(QString s)    //s is 8 bits
{
    //?????
}

Thank you for your reply.

Out of curiosity, how did you come by a "binary string" in the first place? — Russell Borogove
– Russell Borogove, Commented Apr 5, 2012 at 23:57
And did you want to save those 1s and 0s as bits or bytes? Your thought process isn't clear here. — Mooing Duck
– Mooing Duck, Commented Apr 5, 2012 at 23:59
@RussellBorogove It is an int array encoded with Huffman. So I've first stored the Huffman frequency table and then I want to save this code. — goldfrapp04
– goldfrapp04, Commented Apr 5, 2012 at 23:59
@MooingDuck I want to save them as BYTE. For the binary string I provided, I would first like to save "01100101" as a byte, and then "01010100" as the next byte, and so on — goldfrapp04
– goldfrapp04, Commented Apr 6, 2012 at 0:01
Ah. You are modeling a stream of bits with a stream of ASCII characters. Your life will be better if you write a class or a set of functions to model a stream of bits with a stream of bits packed into an array of bytes or integers. — Russell Borogove
– Russell Borogove, Commented Apr 6, 2012 at 0:03

Kornel Kisielewicz · Accepted Answer · 2012-04-06 00:00:37Z

1

QString has a nice toInt method, that optionally takes the base as a parameter (in your case base 2). Just strip 8 characters to form a new QString, and do str.toInt( &somebool, 2 ).

With no error checking it would be probably:

BYTE QStringToByte(QString s)    //s is 8 bits
{
  bool ok;
  return (BYTE)(s.left( 8 ).toInt( &ok, 2 ));
}

(don't take my word for it though, never wrote a line in Qt in my life)

answered Apr 6, 2012 at 0:00

Kornel Kisielewicz

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1 Comment

goldfrapp04 Over a year ago

Your method works well enough. Thanks! And don't be that pessimistic:)

01100110 · Accepted Answer · 2012-04-06 00:03:02Z

0

You may try boost::dynamic_bitset to write bits to a file.

void write_to_file( std::ofstream& fp, const boost::dynamic_bitset<boost::uint8_t>& bits )
{
     std::ostream_iterator<boost::uint8_t> osit(fp);
     boost::to_block_range(bits, osit);
}

answered Apr 6, 2012 at 0:03

01100110

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2 Comments

Russell Borogove Over a year ago

@KornelKisielewicz "...and now you have two problems."

Kornel Kisielewicz Over a year ago

@Russel, at least not a ProblemFactory :P

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